1. Field of Invention
The invention relates to an automatic transmission installed in a vehicle and, more particularly, to a case structure that houses a speed change mechanism of the automatic transmission.
2. Description of Related Art
As one form of the vehicular automatic transmission, there exists an automatic transmission for a front-engine front-drive (FF) vehicle or a rear-engine rear-drive (RR) vehicle. This type of automatic transmission is normally connected in series to an engine between right and left side wheels of a vehicle in a transverse layout such that an axis of the automatic transmission extends parallel to an axle. Therefore, the type of automatic transmission normally adopts a three-axis transaxle construction in which a counter gear mechanism and a differential device are disposed in a single case.
In the three-axis automatic transmission, a counter drive gear for transmitting the output of a speed change device disposed on a main shaft to a counter shaft extending parallel to the main shaft is disposed on the main shaft. Since the counter drive gear transmits large torques produced through speed reductions, it is a normal practice to adopt a construction in which the counter shaft is firmly supported at its center axis to the case. If the counter drive gear is disposed in an intermediate portion of the speed change mechanism, the counter drive gear is supported to a center support that is provided integrally with the case. As an automatic transmission employing the aforementioned supporting method, there is a technology disclosed in U.S. Pat. No. 4,994,007. In this technology, an intermediate portion of a case in a direction along an axis of the case is provided with a support wall extending from a peripheral wall of the case radially inwards. Therefore, in order to assemble a speed change mechanism into the case, the technology adopts a construction in which both a front end portion and a rear end portion of the case have openings, and the opening of the rear end portion is covered with a rear case after the component parts of a rearward half portion of the speed change mechanism have been assembled.
However, if the case body and the rear case are separately provided as in the above-described conventional art, the joint portions of the two case parts need to have thick-walled portions through which fixing devices such as bolts or the like are inserted. The thick-walled portions cannot be protruded to an immediate vicinity of peripheral walls of members of a speed change mechanism or protruded inwardly from a peripheral wall of the case disposed on the peripheral walls, so that the thick portions are protruded outwardly of the outer periphery of the case.
In a typical automatic transmission, a valve body for controlling the speed change mechanism is mounted on the cases so as to extend in parallel to the speed change mechanism. The thick wall portions protruded outwardly from the case as described above, become obstacles against the valve body. The length of the valve body is limited to such a length relative to the entire length of the case that the valve body is disposed inwardly of the joint portions. The area is correspondingly limited. As the area of the valve body decreases, the thickness increases. Therefore, there occur problems in securing a minimal ground clearance of the vehicle and interference with other auxiliary devices.
The invention provides a case structure of an automatic transmission, wherein a rear case may be formed together with a case body so that a valve body mounting face can be secured substantially throughout the entire length of the case.
To achieve the aforementioned, the invention may provide a vehicular automatic transmission including a case, a speed change mechanism disposed around an input shaft, a gear for transmitting an output of the speed change mechanism to a shaft extending along the input shaft, and a support wall attached to the case and supporting the gear. The case may have, at one end of the case, a rear cover portion formed integrally with the case, and may have at another end of the case an opening portion. The support wall may be removable from the case via the opening portion.
The vehicular automatic transmission of the invention allows the support case needed for the speed change mechanism to be disposed in the case and, at the same time, adopts integration of a rear case portion with the case and thereby eliminates a protrusion of a joint portion radially outward relative to the case. Therefore, it becomes possible to secure a valve body-disposing surface substantially throughout the entire length of the case. Hence, restrictions of the area of the valve body can be eliminated.
In the vehicular automatic transmission, a construction may also be adopted wherein the case has, at a mounting position of the support wall and a position of the opening portion, end surfaces that face toward the opening portion and that are shifted from each other in position in a circumferential direction. The support wall may be provided with a protruded portion that can be moved past an end surface of the opening portion of the case and that contacts an end surface provided at the mounting position of the support wall. The support wall may be fixed to the case, with the protruded portions set into contact with the end surface at the mounting position. The opening portion of the case may be closed by a cover that is placed in contact with the end surface of the opening portion and fixed the end surface to cover the opening portion.
The above-described construction makes it possible to place the support wall into the case while disposing the end surface for fixing the support wall to the case and the end surface for fixing the cover for closing the case opening to the case, in portions having substantially equal diameters, since the end surfaces are shifted from each other in the circumferential directions relative to the case. Therefore, it becomes unnecessary to expand the outside diameter of the opening portion side of the case in order to place the support wall. Hence, the outside diameter thereof can be reduced, so that not only the length in the directions of the axis of the case for disposal of the valve body, but also an installation space, can be secured.
Another construction may also be adopted wherein the case has spline teeth that extend in an inner periphery of a peripheral wall of the case in a direction of an axis thereof so as to support a friction member of a brake of the speed change mechanism in such a manner that the friction member is stopped from turning. The spline teeth include short spline teeth that terminate at the mounting position of the support wall and long spline teeth that extend to and terminate at the opening portion of the case. The support wall has an outside diameter portion whose diameter is smaller than a diameter of an inner periphery defined by the long spline teeth, and a protruded portion that protrudes from the outside diameter portion so that the protruded portion can pass through a space between the long spline teeth and can contact an end surface of at least one of the short spline teeth. The support wall may be fixed to the case, with the protruded portion stopped by the end surface of the at least one of the short spline teeth. The opening portion of the case may be closed by a cover that is stopped by and fixed to an end surface of at least one of the long spline teeth to cover the opening portion.
In the above-described construction, the end surface for fixing the support wall to the case and the end surface for fixing the cover for closing the case opening to the case are formed by utilizing the end surfaces of the spline teeth provided for the brake of the speed change mechanism. Further, the inter-teeth spaces between the spline teeth are utilized as insert spaces for bringing the support wall through the opening portion. Therefore, it becomes possible to place the support wall by utilizing the spaces needed for placing and supporting a friction member of the brake of the speed change mechanism, thereby eliminating the need to increase the size of the case for placement of the support wall. Therefore, this construction also makes it unnecessary to expand the outside diameter of the opening portion side of the case in order to place the support wall. Hence, the outside diameter thereof can be reduced, so that not only the length in the directions of the axis of the case for disposal of the valve body, but also an installation space, can be secured.
In the above-described construction, it is also possible to adopt a construction wherein the support wall has an annular protrusion that is fittable to an inner periphery defined by the spline teeth of the case.
In this construction, the support wall can be centered and positioned to the case by fitting the annular protrusion of the support wall to the inner periphery defined by the spline teeth of the case. Therefore, it becomes possible to achieve reliable concentricity of the gear supported by the support wall relative to the input shaft.